What are the risk factors for anal cancer?
A risk factor is anything that affects a person’s chance of getting a disease. Although the exact cause of anal cancer is not known, most anal cancers seem to be linked to infection with HPV (human papilloma virus). Still, most people with HPV infections do not get anal cancer. The risk factors for anal cancer are listed below. But risk factors don’t tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get cancer. Also, people without risk factors can still get cancer.
Risk factors for anal cancer
HPV (human papilloma virus)
Most squamous cell anal cancers seem to be linked to infection by the human papilloma virus (HPV), the same virus that causes cervical cancer. In fact, women who have had cervical cancer (or pre-cancer) have an increased risk of anal cancer.
HPV is a group of more than 100 related viruses. There are several subtypes of the virus, but the one most likely to cause anal cancer is called HPV-16. HPV-16, as well as HPV-18, HPV-31, HPV-33, and HPV-45 are called high-risk types of HPV because they are strongly linked to cancer. They can also cause cancers of the cervix, vagina, and vulva in women, cancer of the penis in men, and throat cancer in both women and men..
It can be very hard to avoid being exposed to HPV. The virus is spread from one person to another during skin-to-skin contact with an infected area of the body. HPV can be spread during sex -- including vaginal intercourse, anal intercourse, and oral sex. It is even possible for a genital infection to spread through hand-to-genital contact.
An HPV infection also seems to be able to be spread from one part of the body to another. This means than an HPV infection may start in the genitals and then spread to the anus.
Infection with HPV is common, and in most cases the body is able to clear up on its own. But in some cases the infection does not go away and becomes long lasting (chronic). Chronic infection can eventually cause certain cancers, including anal cancer.
For men, the 2 main factors that impact the risk of genital HPV infection are circumcision and the number of sex partners. Men who are circumcised (have had the foreskin of the penis removed) have a lower chance of getting and staying infected with HPV. The risk of being infected with HPV is also strongly linked to having many sex partners (over a man’s lifetime).
In women, HPV infections occur mainly at younger ages and are less common in women over 30. The reason for this is not clear. A woman’s risk is increased if she has sex at an early age and has many sexual partners.
Although women who have had many sexual partners are more likely to get infected with HPV, a woman who has had only one partner can still get infected. This is more likely if she has a partner who has had many sex partners or if her partner is an uncircumcised male.
In a study that looked at risk factors for anal HPV infection in women, risk was increased in younger women and in those who had more than 5 sexual partners in their lifetime. Ever having anal sex also increased risk.
Condoms can provide some protection against HPV, but they do not always prevent infection. For more information about HPV and HPV vaccines, see Human Papilloma Virus and HPV Vaccines FAQ.
Ever having cancer of the cervix, vagina, or vulva is linked to an increased risk of anal cancer. This is likely because these cancers are also caused by infection with HPV.
People who have the human immunodeficiency virus (HIV), the virus that causes AIDS, are much more likely to get anal cancer than those who don’t.
Having many sex partners increases the risk of HIV and HPV infection. Having anal sex is a risk factor for anal cancer in both men and women, especially for those under the age of 30.
Current smokers are several times more likely to have cancer of the anus compared with people who never smoked. Quitting smoking reduces this risk. People who used to smoke but have quit are only slightly more likely to get anal cancer compared with people who never smoked.
Weakened immune system
People with weak immune systems are at higher risk for anal cancer. This includes people who have had transplants and who must take drugs to suppress their immune systems.
Race and gender
Anal cancer is more common in African-Americans than in whites. Overall, it is more common in women than men, but in African Americans it is more common in men than in women.
Last Medical Review: 01/14/2013
Last Revised: 01/17/2013